content: /**
   * Copyright (c) 2016-present, RxJava Contributors.
   *
   * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in
   * compliance with the License. You may obtain a copy of the License at
   *
   * http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software distributed under the License is
   * distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See
   * the License for the specific language governing permissions and limitations under the License.
   */
  
  package io.reactivex.flowable.subscribers;
  
  import org.reactivestreams.Subscription;
  
  import hu.akarnokd.reactivestreams.extensions.RelaxedSubscriber;
  import io.reactivex.flowable.internal.subscriptions.SubscriptionHelper;
  import io.reactivex.flowable.internal.utils.EndSubscriberHelper;
  
  /**
   * Abstract base implementation of a {@link org.reactivestreams.Subscriber Subscriber} with
   * support for requesting via {@link #request(long)}, cancelling via
   * via {@link #cancel()} (both synchronously) and calls {@link #onStart()}
   * when the subscription happens.
   *
   * <p>All pre-implemented final methods are thread-safe.
   *
   * <p>The default {@link #onStart()} requests Long.MAX_VALUE by default. Override
   * the method to request a custom <em>positive</em> amount.
   *
   * <p>Note that calling {@link #request(long)} from {@link #onStart()} may trigger
   * an immediate, asynchronous emission of data to {@link #onNext(Object)}. Make sure
   * all initialization happens before the call to {@code request()} in {@code onStart()}.
   * Calling {@link #request(long)} inside {@link #onNext(Object)} can happen at any time
   * because by design, {@code onNext} calls from upstream are non-reentrant and non-overlapping.
   *
   * <p>Use the protected {@link #cancel()} to cancel the sequence from within an
   * {@code onNext} implementation.
   *
   * <p>Like all other consumers, {@code DefaultSubscriber} can be subscribed only once.
   * Any subsequent attempt to subscribe it to a new source will yield an
   * {@link IllegalStateException} with message {@code "It is not allowed to subscribe with a(n) <class name> multiple times."}.
   *
   * <p>Implementation of {@link #onStart()}, {@link #onNext(Object)}, {@link #onError(Throwable)}
   * and {@link #onComplete()} are not allowed to throw any unchecked exceptions.
   * If for some reason this can't be avoided, use {@link io.reactivex.flowable.Flowable#safeSubscribe(org.reactivestreams.Subscriber)}
   * instead of the standard {@code subscribe()} method.
   * @param <T> the value type
   *
   * <p>Example<pre><code>
   * Flowable.range(1, 5)
   *     .subscribeWith(new DefaultSubscriber&lt;Integer&gt;() {
   *         &#64;Override public void onStart() {
   *             System.out.println("Start!");
   *             request(1);
   *         }
   *         &#64;Override public void onNext(Integer t) {
   *             if (t == 3) {
   *                 cancel();
   *             }
   *             System.out.println(t);
   *             request(1);
   *         }
   *         &#64;Override public void onError(Throwable t) {
   *             t.printStackTrace();
   *         }
   *         &#64;Override public void onComplete() {
   *             System.out.println("Done!");
   *         }
   *     });
   * </code></pre>
   */
  public abstract class DefaultSubscriber<T> implements RelaxedSubscriber<T> {
      private Subscription s;
      @Override
      public final void onSubscribe(Subscription s) {
          if (EndSubscriberHelper.validate(this.s, s, getClass())) {
              this.s = s;
              onStart();
          }
      }
  
      /**
       * Requests from the upstream Subscription.
       * @param n the request amount, positive
       */
      protected final void request(long n) {
          Subscription s = this.s;
          if (s != null) {
              s.request(n);
          }
      }
  
      /**
       * Cancels the upstream's Subscription.
       */
      protected final void cancel() {
          Subscription s = this.s;
          this.s = SubscriptionHelper.CANCELLED;
          s.cancel();
      }
      /**
       * Called once the subscription has been set on this observer; override this
       * to perform initialization or issue an initial request.
       * <p>
       * The default implementation requests {@link Long#MAX_VALUE}.
       */
      protected void onStart() {
          request(Long.MAX_VALUE);
      }
  
  }
  